1. Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus having a compact size and a high magnifying power which is used in a video camera for public use, a video camera for surveillance, and so on.
2. Description of Related Art
Recently, in a field of a zoom lens which is used in a video camera or the like, a video camera of a compact size has become more keenly requested. Generally, in the video camera for public use, a zoom lens of a rear focus type having a four group system in which four groups of lenses are arranged in power arrangement in order of positive, negative, positive and positive from an object side has been a main stream. In this zoom lens having the four lens groups, variation of power is performed mainly by moving a second lens group in a direction of an optical axis, while a first lens group and a third lens group are fixed, and correction of an image plane and focusing following this power variation are performed by a fourth lens.
In the zoom lens of the four group system as described above, it is requested that the zoom lens has a high magnifying power and a wide angle of view, when it is used in the video camera for surveillance. Moreover, it is also required to secure a sufficient back focal length for arranging a prism, for example, in order to cope with the video camera in a three CCD (Charge Coupled Device) system. Under the circumstances, there have been proposed in JP-A-06-337353, JP-A-2004-279726, JP-A-2006-047771, and JP-A-2007-171248, for example, zoom lenses of a four group structure having a power arrangement in order of positive, negative, positive and positive, in which a high magnifying power and a wide angle of view are realized, while a long back focal length is secured.
However, in any of the structures as disclosed in the above described Patent JP-A-06-337353, JP-A-2004-279726, and JP-A-2006-047771, the largest angle of view is about 60° or less, and a further larger angle of view (about 70°, for example) is required. In this case, there is such a problem that when the wide angle of view is realized, it becomes difficult to secure the long back focal length, and it becomes also difficult to obtain the high magnifying power, because fluctuation of aberration is increased.
On the other hand, in JP-A-2007-171248, the long back focal length can be realized, even with the wide angle of view of more than 70°. In JP-A-2007-171248, the third lens group is positive.